After some readings on the first book on Harry Potter, I see why some tell he is just a Nerd, just because of the appearance the book describes. Here is one opinion on how this kind of statement seems to fade away with the growing personality of this character. If you have read the books, you'll notice that Harry is not quite a quiet person, just that in his first years he might had little opportunity to be with others. In the ambiance he lived with his relatives, the Dursleys, a hidden Harry stays there until the great news of being a wizard. That's when he gets along with the wizarding world, willing to learn everything about it, just to be away from the reality he was facing before.
In the first book, Harry is described as a skinny boy with round glasses covered with tape, kind of small for his age, with a distinction of having green eyes and black hair difficult to handle. The first chapters tell that Harry was unfortunate to be living in his aunt's house, being treated as if he didn't exist, as if he is just another to maintain, like they didn't agreed with that. But of course they didn't have other option, caring a person who is going to be a wizard in the time being. They just knew it, and by long experience they took care of the situation the way they considered better....
The thing was those first chapters that showed that boy who is simply put away, as if he didn't fit the world he was in. It wasn't his place, that was for sure. The strange events that revolve over Harry made things worse, and because nobody said why of those events, it was a strange mystery. Seems like Harry didn't care too much about it, but is just simply sad to see some person having that position, and he didn't have something that can help against that situation.
Anyway, his look can perceive another personality on him, but he was only limited on his house. The day of his 11th birthday was where things completely changed. Now that he was ready to face the wizarding world by himself, those limitations were broken. His thoughts and ideas were another and that's when we see a Harry that likes to take risks even if everything was against it, facing new circumstances as he stays in Hogwarts, and revealing the mysteries of Magic that tries to stand against him. Even so, his personality most of the time overcame his appearance, and by every adventure taken from each year, he obtains more about his past. From being in a place no one cares for him to being in a place everyone knows him, Harry Potter as character turns to be a interesting one, who in his real him resembles what many people desires: a world in which everything can be possible with a swing of a wand, or maybe with a firm objective and decided and risky action, and a bunch of resources.
"From one world to another, I wonder how he handled all this...."
"If you ask, I would tell you he sure has a curious mind..."
"...and amazing friends too, all the circumstances met to continue their adventure."
"And you are still thinking how in the first book Harry was prone to challenging proposals..."
"Yeah, not very common, but it was part of his thinking, trying to do things against the rules..."
"Much of it involves him, and also his way of revealing the mystery (not that he would think of breaking rules...)"
"It is..., it just amazing the secrets hidden told in those books, and all the plot..."
"Don't analyze it as if you wanna find something else from the books. You'll find it easier if you think the conditions were presented at the right moment and solved at that moment. He just needed to survive and he was the best resource to make it possible."
"Ok, heheh, Dumbledore had it all planned for sure."